1. Field of the Invention
The present invention relates to batteries. More particularly, the invention comprises a battery which can be manufactured in a variety of shapes and geometries that can better utilize available space in specific applications.
2. Description of the Prior Art
Most high power, high energy density batteries used in the aerospace, defense, electric vehicle and other industries today consist of cylindrical or rectilinear, prismatic-shaped cells used singly, or connected in parallel or series into battery packs, depending on the voltage and current requirements of the mission. These batteries are classified as either primary or secondary depending on the intended use and design of the battery.
In a primary battery, the stored energy is released in an irreversible process, and the battery is depleted when the total energy of the cell is released. A secondary battery is one where the stored energy is released in a reversible process, and the battery is capable of being repeatedly charged and discharged.
Examples of secondary batteries include lead acid, nickel cadmium, and nickel metal hydride batteries, which have found widespread use in the commercial market place as rechargeable electrical power sources for use in tools, starting motors, flash lights, electric vehicles, and a variety of other uses. Aerospace qualified nickel cadmium and nickel hydrogen batteries are used in space and satellite applications to provide renewable sources of electrical energy, recharged with solar panels extended from the satellite structure. Secondary lithium ion batteries are now being introduced as high energy density power sources for both space and electric vehicle applications.
In most of the above examples, the battery consists of multiple cylindrical or prismatic cells built up by connecting these cells into cell packs, usually a rectilinear package similar in form to a standard automobile battery. In the case of the nickel hydrogen batteries, called common vessel batteries, in addition to the electrical connection between cells, there is also a network of tubing that allows pressurized hydrogen to flow from cell to cell. Primary batteries also utilize cylindrical and prismatic cells connected in series or parallel, depending on the voltage and current needs of the application.
A reserve battery is a primary battery that can be stored for long periods of time prior to discharge, requiring some form of activation to bring it to a full operational state. The reserve battery is inhibited from open circuit self-discharge during the pre-activation state by having the electrolyte stored separately from the electrodes or by having the electrolyte infused into the plate stack of the battery in a non-conductive state.
Aerospace and defense applications usually employ a so-called “thermal” battery as a reserve battery. For the thermal battery, the electrolyte permeates the plate stack as a solid state salt and is non-conductive for the range of storage temperatures in the pre-activation state. The thermal battery is activated by the ignition of an internal pyrotechnic that heats the electrolyte salt to a liquid state, wherein the electrolyte is capable of conducting current, thereby activating the battery.
In other reserve battery designs, the plate stack is dry and the electrolyte is stored in liquid form in a separate storage reservoir. Upon activation, the electrolyte is injected into the plate stack, allowing the battery to discharge current into the load attached to the terminals of the battery. In the lithium thionyl chloride reserve battery, for example, an acidic form of the thionyl chloride electrolyte is contained in the separate reservoir and injected into the plate stack to achieve activation.
The bimodal battery (U.S. Pat. No. 6,187,471) is an alternative design of the reserve lithium battery which allows it to function as a low-drain battery during periods of storage, and then, after activation, to function as a very high current battery to meet high power density missions. In the bimodal battery, the plate stack is infused with non-acidic, neutral thionyl chloride based electrolyte which allows it to function as a low-current drain power source. Activation is achieved by injecting and mixing an acid additive that creates an acidic form of the electrolyte in the plate stack. The acid electrolyte allows the battery to function as a very high current power source for a relatively short period of time.
Both thermal and thionyl-chloride reserve batteries are used in aerospace and defense applications to power missile and launch vehicle electronics, ignition of pyrotechnics for staging and separation, electric actuators for moving fins and control surfaces, and passive and active on-board sensors. These applications require heavy current for a limited duration of time.
Secondary batteries are used, once a satellite has been launched into space, to continuously power the electronics, the telecommunication data links and sensors. These batteries can be recycled in space for multi-year missions using large solar arrays to recharge the batteries.
Many of the high energy density, high power density batteries used for aerospace and defense create high levels of thermal energy and internal pressure during their operation. These effects are taken into account when designing batteries, such as thermal management techniques to remove heat from the core of the battery, and special pressure containment vessels and relief valves to manage internal pressure buildup. As a result of these thermal and pressure requirements, system designers are often constrained by the form and fit factors of the batteries designed for aerospace applications.
Thin flat-plate and conformable batteries have been developed in the commercial electronics industry to maximize packaging density, allowing system designers to efficiently add the battery to the electronics system without having to design the electronics package around the shape of the battery. Cell phones, for example, have snap-on batteries with relatively thin rectilinear shapes. Thin-line button cells are used in watches to conform to the shape of the watch. These batteries, however are not required to deliver the high currents required in the aerospace applications cited heretofore. What is needed in the aerospace and defense industry are battery concepts that give the aerospace engineer or missile designer the same design flexibility, to efficiently fit the battery into the electronics environment without having to distort that environment.